May, 1913. 



KNOWLEDGE. 



181 



plants towards the north has caused the present flora to be 

 very complex. The connection of the country with the 

 northern, north-eastern, south-eastern, and southern parts of 

 the Asiatic continent made paths for arctic and tropical plants 

 into Japan ; the interruptions between the various islands are 

 bridged over to some extent by currents and wind. Evergreen 

 trees and shrubs and many other tropical plants found their 

 way northwards and became acclimatised to the colder winter 

 night and contented with comparatively high temperature 

 during the day, and above all the warm and moist atmosphere 

 during the summer ; while those coming from the north or 

 north-west, where they were accustomed to a severe winter, 

 migrated up the mountains until they obtained the necessary 

 climatic conditions. Investigations of the Tertiary fossil plants 

 of Japan, Amurland, and North America, show that the 

 present flora originated in the large common flora of the 

 northern region of the Far East. One striking feature is that 

 the flora of the north-east part of Japan bears a striking 

 relationship to that of the Atlantic coast of North America. 

 This was noticed by Asa Gray, who compared the two floras 

 and showed that more than sixty per cent, of Japanese plants 

 grew on the eastern coast of North America, or were 

 represented by closely-related species, while only thirty-seven 

 per cent, grow on the western coast. His suggestion that the 

 close affinity between these floras originated in the Tertiary 

 period has been borne out by further geological evidence, and 

 Engler and other phytogeographers have concluded that the 

 two regions were actually connected, and had a similar 

 climate and flora. After the glacial period many plants 

 which migrated towards the south returned northwards and 

 formed the foundation of the present flora of Japan, while in 

 North America a change in climate had taken place between 

 that of east and west — in the west the climate became dry and 

 mild, and caused great alteration in the flora, in the east little 

 change has taken place and many old species have been 

 preserved. 



Apart from the northern islands, however, the vegetation 

 of Japan shows little actual resemblance to that of North 

 America. Although the same or closely allied plants occur in 

 both regions, they are not found in the same proportion. For 

 instance, in Japan, Tsuga forms continuous and almost 

 unbroken forests of great extent on the mountain slopes, above 

 one thousand six hundred metres from sea level, while in 

 North America this tree is rarely found except scattered in 

 small groves, or as individuals in the deciduous forests ; on 

 the other hand, Picea and Abies, which, in America, form 

 immense forests almost to the exclusion of other species, in 

 Central Japan grow singly or in small groves on the lower 

 border of Tsuga forests, or mingled with broad-leaved trees. 

 In northern Japan and on the high mountains of Honto, 

 birches are more abundant than they are in the northern 

 forests of America, and the river banks in the north, like 

 those of North Europe and Siberia, are lined with arborescent 

 willows and alders, which are rare in eastern North America, 

 where these genera are usually represented by trees. More- 

 over, the numbers given in Gray's estimate should be reduced 

 slightly, since he included as natives some Chinese and Corean 

 plants cultivated in Japan. Besides these and some endemic 

 species, the flora of Japan includes many plants of the boreal 

 region of the old world. For instance, Asperula odorata, 

 which occurs in Europe but not in America, is abundant in 

 North Japan. In South Japan, many tropical and sub-tropical 

 elements may be seen ; certain plants growing in the central 

 and southern parts of the country have also a close affinity to 

 those of South China, as well as to those of the Himalayas. 



The vegetation of Japan may conveniently be arranged in 

 three divisions mainly based on the climatic conditions — (1) 

 Northern Region, extending from 38° N. Lat. northwards to 

 the Kuriles and Saghalien ; with the northern part of Corea ; 

 (2) Middle Region, including the greater part of Honto and 

 Shikoku, part of the north of Kyushu, and South Corea ; (3) 

 Southern Region, including the southern parts of Kii and 

 Shikoku, the greater part of Kyushu, the Bonin islands, the 

 Loochoos, Formosa, and the Pescadores. Within each of 

 these regions the northern and southern portions show certain 

 differences in the vegetation. The northern part of the 



Northern Region is represented by the arctic, and the southern 

 part by the sub-arctic, with a few elements of the cold 

 temperate flora ; in the northern part of the Middle Region 

 the plants of the cold temperate flora are found, in its 

 southern part those of the warm temperate ; the Southern 

 Region has warm temperate and sub-tropical plants in its 

 northern part, and tropical plants in the southern. 



(1) Northern Region. — The sea coasts are lined partly with 

 sand-dunes and partly with cliffs ; salt marshes are but 

 poorly developed. Lists are given for these formations ; the 

 exposed parts of the cliffs show many interesting arctic species 

 of Androsace, Artemisia, Draba, Empetrum, Erigerou, 

 Salix, Saxifraga, Sedum, and so on. Lists are also given 

 for the dry hillsides, humid places in the mountain valleys, 

 the Sphagnum bogs (not much in evidence in the other 

 regions, but here fairly well developed), the ponds and lakes, 

 and the forests. The characteristic forest trees are deciduous 

 oaks, birches, cherries, elm, hornbeam, maples, poplars, 

 Cercidiphyllum (a peculiar tree, the sole representative of 

 the family Cercidiphyllaceae, and closely resembling Ginkgo 

 in general appearance), and various willows in damp places; 

 conifers are represented by a few species of Abies, Juuiperus, 

 Larix, Picea, Taxus and Thujopsis, pines being rare — the 

 only wild species is the small P. putnila, usually on mountain 

 summits. Even in Saghalien and the Kuriles there are 

 various woody climbers (species of Celastrus, Hydrangea, 

 Rhus, Vitis, and so on), growing in tropical luxuriance — the 

 abundance of these plants in Japan has been attributed to the 

 undergrowth of bamboos which cuts off the light and makes 

 the plants climb up the trunks of other trees. On the high 

 peaks, not much over two thousand three hundred metres, 

 there are interesting arctic plants like Bryanthus and 

 Pliyllodoce, generally on exposed rocks. 



(2) Middle Region. — This region is very extensive and 

 mountainous, hence the vegetation is varied. The coasts are 

 lined by pines (Pinus thunbergii and so on) and many dune 

 plants : rocky cliffs are infrequent, and show a poorer vegeta- 

 tion than in the Northern Region. The forest trees show 

 great variety ; evergreens occur largely, and broad-leaved 

 species are especially numerous; there are many conspicuous 

 spring-flowering species of Azalea, Prunus, Pyrus, and so 

 on. More species of Pinus appear in this region, and Crypto- 

 rneria flourishes here, while the tall bamboos (mostly species 

 of Pliyllostachys) form a special feature of the vegetation, 

 being mostly under cultivation and forming dense groves. 

 This region contains the great mountain ranges with 

 perpetual snow in the gulleys, and their flora shows 

 ascending zones of vegetation — illustrated by reference to 

 Fujiyama, the highest volcano in Japan. The gently sloping 

 basal zone, up to three thousand feet, consists of lava and 

 cinders, and is largely covered with grasses, brambles, roses, 

 and bracken, with numerous herbaceous phanerogams, and in 

 places various trees ; this passes into the tree zone, divided 

 into a lower belt with deciduous trees (maples, alders, birches, 

 hornbeam, oak, and so on) and many shade-loving plants in the 

 undergrowth, and a higher conifer belt in which Abies firma 

 appears first, and is followed by Larix, Picea, Tsuga, and so 

 on. Above two thousand metres, the gradient becomes 

 steeper, and trees are less abundant, the approach to the 

 shrub zone being marked by rowan, rhododendron, alders, 

 stunted birches, shrubby Spiraea, dwarf willows, and various 

 Ericaceous shrubs, with herbaceous species of mostly alpine 

 character. The zone from seven thousand five hundred to 

 ten thousand feet belongs to the alpine region, with typically 

 alpine and arctic plants ; above this to the summit (about 

 thirteen thousand five hundred feet) is the lichen zone with 

 Cetraria islandica, Cladonia rangiferina, Rhizocarpon 

 geographicum, and so on. The alpine zone of Fujiyama 

 does not contain many plants, though a few are known only 

 from this mountain, but on the other mountains of Central 

 Japan, which form the backbone of the main island, and are 

 often called the Japanese Alps, alpine vegetation is well 

 developed. On these mountains a creeping pine (P.pumila), 

 also found in Siberia, appears in the shrub zone and extends 

 to the alpine zone ; many interesting plants are found in the 

 shade of the thickets of this pine. Many arctic plants found 



